In a steam reformer, under high temperatures (e.g., 400-800° C.) and in the presence of a catalyst (e.g., nickel), steam may react with a feed gas (e.g., methane) to generate a reformate (e.g., hydrogen) which may be used as fuel in a hydrogen fuel cell to generate electricity, for example. In some examples, a mixture of hydrogen and carbon monoxide is generated in a main reaction chamber of the steam reformer. The hydrogen and carbon monoxide are mixed with steam and are passed through an auxiliary reaction chamber to further an extent of production of hydrogen in what is known as a water-gas shift (WGS) reaction.
The WGS reaction is highly exothermic and an auxiliary reaction chamber temperature increases as a result. In a circular or annular reaction chamber, the heat produced by the WGS reaction may be dissipated though an outer wall of the auxiliary reaction chamber and through gas exiting the auxiliary reaction chamber. Due to heat loss at the outer wall and uneven flow distribution, local hot zones may exist within the reaction chamber resulting in degradation of the catalyst at the hot zones. In some examples, the auxiliary reaction chamber may be operated at a lower temperature, however, the catalyst is less active and more catalyst is required, thereby increasing a size of the system.